Electric brush and brush holder assembly



Dec. 21, 1965 J. E. DIEHL ELECTRIC BRUSH AND BRUSH HOLDER ASSEMBLY 3 Sheets-Sheet 1 Filed Sept. 4, 1963 INVENTOR. JOHA/ Dish/4,.

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Dec. 21, 1965 J. E. DIEHL 3,225,234

ELECTRIC BRUSH AND BRUSH HOLDER ASSEMBLY Filed Sept. 4, 1963' 5 Sheets-Sheet 2 INVENTOR. JOHN .E. DIE/41..

Dec. 21, 1965 J. E. DlEHL ELECTRIC BRUSH AND BRUSH HOLDER ASSEMBLY 3 Sheets-Sheet 3 Filed Sept. 4, 1963 INVENTOR Jo/m/ 6 0.25/11.

United States Patent f 3,225,234 ELECTRIC BRUSH AND BRUSH HOLDER ASSEMBLY John E. Diehl, Stackpole Carbon (10., St. Marys, Pa. Filed Sept. 4, 1963, Ser. No. 306,988

Claims. (Cl. 310-246) This invention relates to electric brushes and their holders, and more particularly to an assembly that can be used with current collectors that are rotatable in either direction. This application is a continuation-in-part of my copending application, Serial No. 264,092, filed March 11, 1963, now abandoned.

One of the most common causes of short brush life and of unsatisfactory machine performance is the use of mechanically unstable brushes. They vibrate and chatter in their holders, chip, break, and shift position when the current collector is reversed. Various attempts have been made to meet these difiiculties and a few have been quite successful, but even under the best conditions the brushes wear out much sooner than desired. This problem arises because practically all brushes are straight and many have to be mounted in confined spaces so that their length is limited materially. In an attempt to solve the problem it has been proposed heretofore that the brushes be curved lengthwise so that they can extend part way around the current collector in the space between it and its enclosure. This permits the brushes to be made considerably longer than heretofore. Nevertheless, full advantage of the increased length of such brushes has not been taken because, due to their shape, the means that press them against the current collectors have become ineffective for that purpose while a considerable length of brush remains. In other words, as wear consumes the curved brushes it has not been possible to move their outer ends as close to the collector as could be done with straight brushes, and the spring pressure against the brushes has decreased with reduction in brush length. The problem of holding a brush steady so that it will not vibrate or change position, especially when the current collector is designed to rotate in either direction, has been more difiicult to solve in the case of curved brushes than with straight brushes. The result of all this is that curved brushes have not found much acceptance, even though they can be made much longer than straight brushes for the same machine.

It is among the objects of this invention to provide a relatively simple and inexpensive curved brush and brush holder assembly which is suitable for all types of brushusing machines, which can satisfactorily replace radial, trailing and reaction or leading brushes now used, and in which, regardless of direction of rotation of the current collector, the brush is maintained in an exactly fixed position relative to the periphery of the collector under all circumstances. A further object is to provide such an assembly, in which the curved brush can be mounted facing in either direction around the collector, regardless of which direction the other brushes are facing. Other objects are to provide such an assembly, in which most of the length of the curved brush can be utilized, and in which the brush is held against the collector under a substantially constant pressure regardless of the length of the brush and without adjustment. A further object is to provide such an assembly, in which the brush has a minimum parasitical mass for a given useable brush length, and which is readily accessible for quick replacement. An additional object is to provide such an assembly, in which the wearing face of the brush always remains substantially radial to the collector.

In accordance with this invention the brush holder has an arcuate wall With a longitudinally concave inner surface. Suitable means are provided for supporting the 3,225,234 Patented Dec. 21, 1965 holder with its inner end adjacent a current collector. The arcuate wall of the holder is provided with a slot through it, which extends from a point adjacent its inner end to the opposite end of the holder. Fitting against the inner surface of the holder and slidable lengthwise of it is the longitudinally convex outer surface of an arcuate brush. The brush projects from the inner end of the holder into engagement with the current collector. There are separate connecting members secured to the inner end of the holder and the outer end of the brush. Supported by one of these members is a constant pressure spring in the form of a spiral coil of metal tape, the outer end of which is unwound and fastened to the other connecting member. The portion of the tape between its outer end and the coil extends along the convex brush surface and the slot, with the inner end of that portion of the tape disposed between the coil and brush. Consequently, the tendency of the spring tape to maintain itself coiled will hold the brush against the inner surface of the holder and will pull the outer end of the brush toward the inner end of the holder as the brush wears. Preferably, the arc of the holder has a radius intersecting the collector surface at a point midway between the opposite edges of the brush contact face at an angle between 5 and 20 with a line tangent to the collector surface at said point, the center of the arc being located at the collector side of the tangent line.

The invention is illustrated in ings, in which FIG. 1 is a side view of my brush holder and brush assembly, partly in section;

FIG. 2 is a view taken from the coil end of the assemy;

FIG. 3 is a view from the opposite end of the assembly, with the brush shown partly in section;

FIG. 4 is a central fragmentary vertical section of a modification;

FIG. 5 is a view, similar to FIG. 4, of another embodiment of the invention;

FIG. 6 is a side view of a further modification;

FIG. 7 is a view, partly in section, taken from the coil end of the assembly shown in the preceding figure;

FIG. 8 is a view, similar to FIG. 1, of still another modification; and

FIG. 9 is a plan view of the brush and holder in FIG. 8.

Referring to FIGS. 1, 2 and 3 of the drawings, a brush holder is mounted beside a rotating cylindrical electrical collector 1, such as the commutator or slip ring of a rotat able electrical machine( not shown). For convenience of description only, the rotating collector will be referred to herein as a commutator. The machine is reversible, so that the commutator can be rotated in either direction. The brush holder or guide is channel shape, with an arcuate web or wall 2 and parallel side flanges 3. The arcuate wall has a longitudinally concave inner surface and preferably extends at least in the plane of rotation of the commutator. The inner end of the holder is disposed substantially radially of the commutator, from which it is spaced a short distance. The holder may be supported in any suitable manner, such as, for example, by a rod 4 secured to one side of it and rigidly supported by suitable means, such as the frame 6 of the machine. The arcuate wall 2 of the brush holder is provided with a central slot 5 through it extending from a point near the inner end of the holder to its opposite end.

The carbon or graphite brush 7 that is mounted in the holder is curved like it and preferably extends through an arc of about The brush has a uniform thickness and parallel curved inner and outer surfaces, with the outer convex surface fitting against the inner arcuate surface of the brush holder, against which the brush can slide lengththe accompanying drawshown in FIG. 1.

wise when it is rotated about its axis. The opposite sides of the brush slide against the side flanges of the holder, and the inner end of the brush projects from the inner end of the holder into engagement with the commutator as The outer end of the brush carries shunt wires 8, by which it can be connected into an electric circuit.

In order to hold the inner end of the brush against the commutator and to maintain the brush in firm engagement with the arcuate wall of the holder at all times so that the brush will not vibrate and chatter, regardless of which direction the commutator is turning, a constant pressure spring is used which is in the form of a spiral coil of metal tape 11. Such a spring in itself is a well-known commercial item and is called a Negator spring. The spring tape of such a coil is so formed that it tends to curve transversely. Although this curvature generally is visible only in the short length of spring between the coil and the point of contact with the brush, to make it clear that the tendency to curve is there the surface of the coil in FIG. 2 has been shown transversely convex in a greatly exaggerated manner. No matter how far the outer end of the tape is pulled away from the coil, the tape will always exert essentially the same amount of effort to recoil itself and therefore the spring exerts the same pull or constant pressure, as is well known. This constant pressure spring coil is rotatably supported by a bracket 12 connected to the inner end portion of the brush holder and projecting outwardly from its arcuate wall at opposite sides of slot 5. Preferably, the coil is mounted on a spool 13 that is rotatably mounted on a pin 14, the opposite ends of which are rigidly mounted in the opposite sides of the bracket. Spacing sleeves 15 may be loosely mounted on the pin to hold the spool at the center of the pin.

The coil is positioned in the bracket in such a manner that when the outer end of the tape is pulled toward the outer end of the holder, the unwound portion of the tape will extend between the coil and the adjacent holder and brush. In other words, as viewed in FIG. 1 the tape is unwound from the bottom of the coil in a counterclockwise direction, rather than from the top of the coil in a clockwise direction. This is very important as will soon be explained. The outer end portion of the tape is pulled from the coil and around the outside of the brush to its outer end, where a U-shape metal clip 17 connected to the end of the tape is slipped over the end of the brush. Consequently, the tape follows the curvature of the brush and lies against its convex surface from the inner end of the holder slot to the outer end of the brush.

Wrapping the spring tape around the brush more or less flattens the tape transversely, but the tendency of the tape to resume its transverse curvature, coupled with the pull of the tape against the outer end of the brush, produces forces that continually press the brush against the curved wall 2 of the holder and radially against the collector, regardless of the length of the brush and the direction of rotation of the commutator. The brush therefore has stability under all conditions of friction and rotation. The end clip can be pulled around the brush holder as far as the dotted line position in FIG. 1 as the brush wears, and it still will press the brush against the commutator and the curved wall of the holder. Since a constant pressure spring is used, the brush always exerts the same pressure against the commutator. Moreover, in view of the fact that the brush depends on only one brush holder surface for support and guidance, the assembly utilizes the same principle of operation as reaction and trailing type brush holders to provide brush stability. This stability is obtained whether the assembly is used with unidirectional or bidirectional electric machines.

It will be seen that a series of these brushes around a commutator can be mounted facing either direction or Cit in both directions, without impairing their operation. This feature eliminates many design and application problems in machines having certain areas outside the commutator surface which are partially closed or which are fully open but not uniformly spaced. The brush holders can be mounted in pairs back to back, which cannot be done with either leading or trailing type brush holders. The curved brush can extend for more than if desired, but from a cost standpoint it should be no more than 180". It is well known that optimum performance and brush life cannot be obtained while employing a force-applying means, the pressure of which varies with the brush length, but that problem does not arise with my constant pressure brush. Since the brush holder does not require levers, pads, pressure fingers and other elements used by conventional brush holders, my brush possesses the minimum inertia for a given useable brush length and thus allows the brush to respond to any collector eccentricities most rapidly and, because this provides continuous and more uniform electrical contact to be made with the collector, results in improved machines and brush performance. The open side of the brush holder permits the brush to be quickly and easily removed and replaced and allows the holder to be cleaned readily.

In the modification shown in FIG. 4, the side flanges of the arcuate brush holder 20 have been omitted and their place taken by a pair of parallel arcuate guide ribs 21 that project from the inner surface of the holder at opposite sides of its slot 22 into grooves 23 in the arcuate brush 24, which is engaged by a spring tape 25. These ribs and grooves guide the brush in a straight line as it wears and prevent it from moving sideways in the holder. Otherwise, the assembly is the same as shown in FIG. 1.

In the embodiment of the invention shown in FIG. 5, only one guide rib 27 is used and this is a short one extending from the center of the inner end of the slot 28 to the inner end of the arcuate brush holder 29. The outer side of the brush 30 is provided with a central groove 31 extending throughout its length for receiving the guide rib so that the brush cannot move laterally in the holder. A spring tape 32 extends around the outside of the brush.

In the further modification shown in FIGS. 6 and 7, the constant pressure spring coil 35, the transverse curvature of which has been greatly exaggerated in FIG. 7, 18 attached to the outer end of the arcuate brush 36 instead of to the inner end of the slotted arcuate brush holder 37, and the outer end of the spring tape 38 is fastened to the inner end of the holder instead of to the outer end of the brush. The spring coil is mounted on a spool 39 that is journaled on a pin 40, the ends of which are mounted in a U-shape bracket 41 fastened by a connecting member 42 to the outer end of the brush. The bracket extends radially outward from the convex surface of the brush. The tape is pulled from between the coil and the lbrush to unwind it and it extends around the convex surface of the brush and through slot 43 to the outside of the inner end of the brush holder. It is fastened by a rivet 44 or other connecting means to the outside of the holder between the inner ends of the slot and holder. The action of the spring is the same as in FIG. 1, except that it is the coil itself that travels with the wearing brush, while the outer end of the spring tape remains in fixed position.

An embodiment of the invention having special advan tages is shown in FIGS. 8 and 9. In this embodiment the electric brush 50 is tilted toward the current collector 51 as compared with the brushes previously described herein. In other words, the outer end of the brush in FIG. 8 is closer to the current collector than is the outer end of the brush in FIG. 1, so the inner and outer edges of the contact face of the brush lie in a plane making an oblique angle with the adjoining portion of the inner surface of the brush. The inner edge of the contact face of the brush forms the leading edge of the contact face while the collector 51 is turning in a counter-clockwise direction, and the same edge forms the trailing edge of the contact face when the collector is rotating in a clockwise direction. Of course, the brush-engaging wall 52 of the brush holder likewise is tilted to the same extent. More specifically, although the brush holder may be the same type as any of those shown in the preceding figures, the curved wall of the one shown in FIG. 8 is not provided with side flanges, but with a central longitudinal guide rib 53 extending between its inner end and its longitudinal slot 54 and projecting into a groove 55 extending lengthwise of the convex surface of the brush. The holder may be supported by a rod 56 or any other suitable means secured to one side of it.

The brush that is mounted in the holder forms a segment of a cylinder and preferably originally forms about a 180 arc. It has a uniform thickness from end to end, except for the guiding groove 55. The brush is held in the holder and against the current collector by a constant pressure spring 57 like the ones described before. The spring coil may be mounted on a spool 58 that is rotatably mounted on a pin 59 supported in a bracket 60, rigidly connected to the inner end portion of the brush holder. The tape is unwound from the bottom of the coil in counter-clockwise direction in FIG. 8, and its outer end may be provided with a hole so that it can he slipped over the head of a pin 61 embedded in the outer end portion of the brush. It will be clear that the flexible tape follows the curvature of the brush and lies against its convex surface. The tendency of the tape to coil up presses the brush against the curved wall of the holder and against the current collector, which can rotate in either direction.

Ordinarily, the inner or contact end of the brush shown in FIG. 1 will be held firmly against the current collector, regardless of its direction of rotation. However, if unusually high frictional forces occur while the collector is rotating in a clockwise direction, or if there is a high commutator bar that strikes the brush, there would be a tendency to push the inner end of the brush to the right end, because of the force component of the spring radially outward around the brush, results in the brush pivoting around the outer end of the brush holder and thereby being thrown out of the holder. Whether or not actual dislodgement of the brush occurs under such circumstances, the inner end of the brush may vibrate horizontally and thereby affect the stability of the brush in an undesirable manner. These tendencies can be avoided by tilting the brush and holder in the manner shown in FIG. 8, because that increases the force with which the inner end portion of the brush is held against the brush holder. They are tilted in such a way that the radius R of the brush intersects the surface of the current collector at a point midway between the leading and trailing edges of the brush contact face at an acute angle between 5 and 20 with a line T that is tangent to the collector surface at that same point. It will be noted that the center C of curvature of the arc formed by the brush holder wall 52, or the center of the cylinder of which the brush is a segment, is located at the collector side of tangent line T. Preferably, the acute angle just referred to is between and The exact angle can vary somewhat, depending upon the type of machine, atmospheric and operating conditions, brush grade, brush radius and current collector diameter. In critical applications a angle may be used to insure good brush stability under all possible conditions without requiring the brush to be shortened unduly. A greater angle would either locate the outer end of the brush so close to the current collector that flashover might occur, or the length of the brush would have to be shortened to an undesirable extent. In other cases a 5 angle may provide as much stability as is needed and also permit a longer brush to be used. An angle between 10 and 15 is a reasonable compromise between stability and brush length.

With the brush in the position just described, it must move concentrically in the holder before its inner end can be moved tangentially away from the adjoining surface of the holder, and that is very difficult for it to do, because any frictional force developed at its contact face would have to exceed the spring force holding the brush against the current collector before the contact face of the brush could be pulled by that frictional force laterally away from the holder. Such a condition is extremely unlikely ever to occur, so this arrangement insures excellent brush stability, ability to follow the collector, and uniformity of electrical contact. Another advantage of tilting the brush is that it permits the brush to be worn to a shorter length than in FIG. 1 before any instability is likely to be encountered.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. An electric brush and brush holder assembly comprising a holder having an arcuate wall with a longitudinally concave inner surface provided with inner and outer ends, means for supporting the holder with its inner end adjacent a rotating current collector, said wall being provided with a slot through it extending from a point adjacent its inner end to the opposite end of the wall, an arcuate brush having a longiutdinally convex outer surface fitting against said inner surface of the holder and slidable lengthwise of it, the brush projecting from the inner end of the holder, a constant pressure spring in the form of a spiral coil of metal tape, and separate connecting members secured to the inner end of the holder and the outer end of the brush, said coil being rotatably supported by one of said members, the outer end of said spring tape being fastened to the other of said members, the portion of the tape between its outer end and the coil extending along said convex brush surface and said slot with the inner end of said portion disposed between the coil and brush, whereby the tendency of the spring tape to maintain itself coiled will hold the brush against the inner surface of the holder and pull the outer end of the brush toward the inner end of the holder as the brush wears.

2. An electric brush and brush holder assembly according to claim 1, in which said holder is channel shape with side guide flanges engaging the opposite sides of the brush.

3. An electric brush and brush holder assembly according to claim 1, in which said inner surface of the holder is provided with a longitudinally extending guide rib, and the convex surface of the brush is provided with a groove receiving said rib.

4. An electric brush and brush holder assembly according to claim 1, in which said inner surface of the holder is provided with a longitudinally extending guide rib at each side of said slot, and the convex surface of the brush is provided with a pair of parallel grooves receiving said ribs.

5. An electric brush and brush holder assembly comprising a holder having an arcuate wall with a longitudinally concave inner surface provided with inner and outer ends, means for supporting the holder with its inner end adjacent a rotating current collector, said wall being provided with a slot through it extending from a point adjacent its inner end to the opposite end of the wall, an arcuate brush having a longitudinally convex outer surface fitting against said inner surface of the holder and slidable lengthwise of it, the brush projecting from the inner end of the holder, a constant pressure spring in the form of a spiral coil of metal tape, means attached to the holder adjacent its inner end and projecting outwardly from said Wall for rotatably supporting the coil, the outer end portion of the tape extending between the coil and holder and outwardly in said slot along said convex brush surface toward its outer end, and means fastening the outer end of the tape to the outer end of the brush, whereby the tendency of the spring tape to maintain itself coiled will hold the brush against the inner surface of the holder and pull the outer end of the brush toward the coil as the brush wears.

6. An electric brush and brush holder assembly comprising a holder having an arcuate wall with a longitudinally concave inner surface provided with inner and outer ends, means for supporting the holder with its inner end adjacent a rotating current collector, said wall being provided with a slot through it extending from a point adjacent its inner end to the opposite end of the wall, an arcuate brush having a longitudinally convex outer surface fitting against said inner surface of the holder and slidable lengthwise of it, the brush projecting from the inner end of the holder, a constant pressure spring in the form of a spiral coil of metal tape, means attached to the brush adjacent its outer end and projecting outwardly from said convex surface for rotatably supporting the coil, the outer end portion of the coil extending between the coil and brush and inwardly along said convex brush surface and slot toward the inner end of the holder, and means fastening the outer end of the tape to the outside of said wall between its inner end and the slot whereby the tendency of the spring tape to maintain itself coiled will hold the brush against the inner surface of the holder and pull the coil toward the inner end of the holder as the brush wears.

7. The combination with a cylindrical current collector rotatable in opposite directions, of an electric brush holder having a wall forming an arc of a circle, said wall having a longitudinally concave inner surface provided with inner and outer ends, means for supporting the holder with said inner end adjacent said collector and with said wall extending circumferentially of the collector, said wall being provided with a slot through it extending from a point adjacent its inner end to the opposite end of the wall, an arcuate brush having a longitudinally convex outer surface fitting against said inner surface of the holder and slidable lengthwise of it, the brush projecting from the inner end of the holder and having an end contact face engaging the cylindrical surface of the collector, said are having a radius intersecting said collector surface at a point midway between the opposite edges of said brush contact face at an angle between 5 and 20 with a line tangent to the collector surface at said point, the center of curvature of said are being located at the collector side of said tangent line, a constant pressure spring in the form of a spiral coil of metal tape, and separate connecting members secured to the inner end of the holder and the outer end of the brush, said coil being rotatably supported by one of said members, the outer end of said spring tape being fastened to the other of said members, the portion of the tape between its outer end and the coil extending along said convex brush surface and said slot with the inner end of said portion disposed between the coil and brush, whereby the tendency of the spring tape to maintain itself coiled will hold the brush against the inner surface of the holder and pull the outer end of the brush toward the inner end of the holder as the brush wears.

8. The combination recited in claim '7, in which said angle is between 10 and 15 9. An electric brush in the form of a segment of a cylinder and having at one end a contact face for engagement with the cylindrical surface of a rotating current collector, the leading and trailing edges of said face lying in a plane making an oblique angle with the adjoining portion of the curved incr surface of the brush, the radius of said brush that intersects said plane at a point midway between said edges makes an acute angle between 5 and 20 to said plane.

10. An electric brush according to claim 9, in which said acute angle is between 10 and 15.

References Cited by the Examiner UNITED STATES PATENTS 3,145,316 8/1964 Page 310-246 ORIS L. RADER, Primary Examiner. 

1. AN ELECTRIC BRUSH AND BRUSH HOLDER ASSEMBLY COMPRISING A HOLDER HAVING AN ARCUATE WALL WITH A LONGITUDINALLY CONCAVE INNER SURFACE PROVIDED WITH INNER AND OUTER ENDS, MEANS FOR SUPPORTING THE HOLDER WITH ITS INNER END ADJACENT A ROTATING CURRENT COLLECTOR, SAID WALL BEING PROVIDED WITH A SLOT THROUGH IT EXTENDING FROM A POINT ADJACENT ITS INNER END TO THE OPPOSITE END OF THE WALL, AN ARCUATE BRUSH HAVING A LONGITUDINALLY CONVEX OUTER SURFACE FITTING AGAINST SAID INNER SURFACE OF THE HOLDER AND SLIDABLE LENGTHWISE OF IT, THE BRUSH PROJECTING FROM THE INNER END OF THE HOLDER, A CONSTANT PRESSURE SPRING IN THE FORM OF A SPIRAL COIL OF METAL TAPE, AND SEPARATE CONNECTING MEMBERS SECURED TO THE INNER END OF THE HOLDER AND THE OUTER END OF THE BRUSH, SAID COIL BEING ROTATABLY SUPPORTED BY ONE OF SAID MEMBERS, THE OUTER END OF SAID SPRING TAPE BEING FASTENED TO THE OTHER OF SAID MEMBERS, THE PORTION OF THE TAPE BETWEEN ITS OUTER END AND THE COIL EXTENDING ALONG SAID CONVEX BRUSH SURFACE AND SAID SLOT WITH THE INNER END OF SAID PORTION DISPOSED BETWEEN THE COIL AND BRUSH, WHEREBY THE TENDENCY OF THE SPRING TAPE TO MAINTAIN ITSELF COILED WILL HOLD THE BRUSH AGAINST THE INNER SURFACE OF THE HOLDER AND PULL THE OUTER END OF THE BRUSH TOWARD THE INNER END OF THE HOLDER AS THE BRUSH WEARS. 